Induced sputum in interstitial lung diseases

Purpose of review Induced sputum is a particularly useful procedure since it provides information on the cellular and molecular constituents in inflammation. Extensive work has demonstrated the application of induced sputum in the management of asthma, chronic obstructive pulmonary disease and chronic bronchitis, but less attention has been paid to its efficacy in diagnosing interstitial lung diseases. This review analyzes the applications of induced sputum in the assessment of sarcoidosis, nongranulomatous interstitial lung diseases, occupational lung diseases and other systemic diseases with or without lung involvement. Recent findings T cell subsets in induced sputum in combination with pulmonary function testing can serve as predictors with high specificity and sensitivity in diagnosing sarcoidosis, using multivariate logistic regression models which can be easily implemented in clinical practice. Differential cell counts in induced sputum are as useful as bronchoalveolar lavage for identifying neutrophilic inflammation in patients with nongranulomatous interstitial lung diseases (e.g. idiopathic, pulmonary fibrosis) and detecting chronic rejection in bronchiolitis obliterans syndrome. Sputum analysis has also been shown to be a useful tool for diagnosing, assessing and monitoring occupational lung disorders. Summary We suggest integrating induced sputum technology to the well-established criteria for the diagnosis of interstitial lung diseases, especially when there are clinical contraindications for performing bronchoscopy or when tissue confirmation is absent for any reason.